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Abstract

Although many lineages of terrestrialized crustaceans have poor olfactory capabilities, crabs in the family Coenobitidae, including the terrestrial hermit crabs in the genus Coenobita, are able to locate food and water using olfactory antennae (antennules) to capture odors from the surrounding air. Terrestrial hermit crabs begin their lives as small marine larvae and must find a suitable place to undergo metamorphosis into a juvenile form, which initiates their transition to land. Juveniles increase in size by more than an order of magnitude to reach adult size. Since odor capture is a process heavily dependent on the size and speed of the antennules and physical properties of the fluid, both the transition from water to air and the large increase in size during ontogeny could impact odor capture. In this study, we examine two species of terrestrial hermit crabs, Coenobita perlatus H. Milne-Edwards and Coenobita rugosus H. Milne-Edwards, to determine how the antennule morphometrics and kinematics of flicking change in comparison to body size during ontogeny, and how this scaling relationship could impact odor capture by using a simple model of mass transport in flow. Many features of the antennules, including the chemosensory sensilla, scaled allometrically with carapace width and increased slower than expected by isometry, resulting in relatively larger antennules on juvenile animals. Flicking speed scaled as expected with isometry. Our mass-transport model showed that allometric scaling of antennule morphometrics and kinematics leads to thinner boundary layers of attached fluid around the antennule during flicking and higher odorant capture rates as compared to antennules which scaled isometrically. There were no significant differences in morphometric or kinematic measurements between the two species.

Author Comment

This manuscript has been submitted to PeerJ.

Additional Information

Competing Interests

The authors have no competing interests to declare.

Author Contributions

Lindsay D Waldrop conceived and designed the experiments, performed the experiments, analyzed the data, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.

Quang V Nguyen performed the experiments, reviewed drafts of the paper.

Field Study Permissions

The following information was supplied relating to field study approvals (i.e., approving body and any reference numbers):

L. Waldrop obtained a scientific permit from the French Polynesia government prior to starting the research. A scan of the original permit including governmental seal has been uploaded as a Supplemental file.

Data Deposition

The following information was supplied regarding the deposition of related data:

Figshare DOI: http://dx.doi.org/10.6084/m9.figshare.1030320

Funding

This work was supported by the Virginia and Robert Gill Chair and a MacArthur Foundation Fellowship (to M. Koehl); the Reskteco and Gray Fellowships from the University of California, Berkeley Department of Integrative Biology to L. Waldrop; Sigma-Xi Grant-in-Aid of Research to the L. Waldrop; and by a Traineeship to L. Waldrop (National Science Foundation Integrative Graduate Education and Research Traineeship [DGE-0903711] to R. Full, M. Koehl, R. Dudley, and R. Fearing); and by a National Science Foundation Research and Training Grant 5-54990-2311 (to R. McLaughlin, R. Camassa, L. Miller, G. Forest, and P. Mucha). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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